In recent years, disk devices such as magnetic disk drives and optical disk drives have widely been used as external storage devices of computers and image recording devices.
As such a disk device, for example, a magnetic disk drive generally comprises a magnetic disk provided in a base, a spindle motor which supports and rotates the magnetic disk, and a suspension assembly which supports a magnetic head. The suspension assembly includes a suspension attached to a distal end portion of an arm, a trace member (a flexure or a wiring trace) provided on the suspension and a load beam. The trace member includes a gimbal portion which supports the magnetic head, forming a head suspension assembly.
In more recent years, there is proposed a suspension assembly wherein a piezoelectric element (PZT element) serving as actuation element is mounted in the vicinity of a gimbal portion of a trace member, and a magnetic head is minutely displaced in a seek direction by expansion and contraction of the piezoelectric element. According to the suspension assembly, the operation of the magnetic head can be minutely controlled by controlling a voltage to be applied to the piezoelectric element.
In the suspension assembly, the piezoelectric element is fixed by its entire surface to the trace member. But when the PZT element expands or contracts, it bends in its thickness direction in some cases, which may produce vibrations in directions crossing the expansion/contraction directions (out-of-plane vibration). The out-of-plane vibration is propagated to the suspension via contact points of the trace member, and may excite resonance of the suspension. As a result, the accuracy of positioning the magnetic head is reduced.